Antistatic agent for polyacetal resins

ABSTRACT

An antistatic agent imparting excellent antistatic property to the polyacetal resins and the polyacetal resins using this antistatic agent. The antistatic agent for polyacetal resins is obtained by including polyalkylene polyols or metal salt-dissolved polyalkylene polyols in a basic carbonate of metals consisting chiefly of alkali metals and aluminum having a porous volume of 0.5 cc/g or larger over a region of meso pores to quasi-macro pores of porous radii of from 200 to 1000 angstroms or in an anion exchanger thereof, said porous volume being greater than 30% of the whole porous volume, and a polyacetal resin composition in which said antistatic agent is blended. The antistatic agent of the invention imparts stable antistatic properties to the above resins and is little dependent upon the environment, and further does not lose thermal property or mechanical strength that occurred with the conventional antistatic agents. Therefore, the resin composition can be extensively used in the field of engineering plastics.

This is a division of application Ser. No. 08/214,500, filed Mar. 18,1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antistatic agent for polyacetalresins exhibiting excellent antistatic effect and to a polyacetal resincomposition using the above agent. More specifically, the inventionrelates to an antistatic agent which imparts stable antistatic effect tothe polyacetal resins and is little dependent upon the environment,without impairing mechanical properties, thermal properties, moldabilityand machinability.

2. Description of the Prior Art

Owing to their excellent mechanical properties, thermal properties,long-lasting properties, abrasion properties, moldability andmachinability, the polyacetal resins have been used as engineeringplastic materials in a broad field of applications such as automobiles,electric and electronic appliances. Like many other plastic materials,however, the polyacetal resins have high surface resistivities causingtroubles that stem from the electrification such as electrostatic noise,surface fouling, and adhesion of matters, depending upon theapplications. In order to eliminate such troubles, a variety ofantistatic agents have heretofore been used.

Such antistatic agents are effective even for the polyacetal. However,the ionic substances, such as anionic and cationic antistatic agents,and a mixture of a polyethylene oxide (PEO) and an alkali metal salt(e.g., Japanese Laid-Open Patent Publication No. 139266/87), are notdesirable since they cause the polyacetal to be discolored and to losethe thermal stability. Nonionic antistatic agents have been proposedgiving little adverse effects, which, however, exhibits generally smallantistatic effect and must be added in large amounts if it is attemptedto decrease the electrification properties down to the practicablelevel.

However, addition of the antistatic agents in large amounts generallycauses the molded articles to lose their mechanical properties,moldability and machinability and, particularly, causes much bleeding onthe surfaces of the molded articles to deteriorate the appearance. Ingeneral applications, furthermore, the antistatic agents have problemsin maintaining antistatic effect and stability, such as losing theantistatic effect when the molded articles are washed with a solvent orare preserved in a low-humidity environment.

SUMMARY OF THE INVENTION

The object of the present invention therefore is to provide anantistatic agent for polyacetal resins, which can be blended withoutdeteriorating the thermal stability, mechanical strength andmachinability of the polyacetal resins, is little dependent upon theenvironment and stably exhibits antistatic property for extended periodsof time.

Another object of the present invention is to provide a polyacetal resincomposition which exhibits excellent antistatic property, excellentproperties inherent in the engineering plastic materials and excellentanti-bleeding property, and does not cause the resin to be colored in aparticular hue.

According to the present invention, there is provided an antistaticagent for polyacetal resins comprising an inclusion product obtained byincluding polyalkylene polyols or alkali metal salt-dissolvedpolyalkylene polyols in a basic carbonate of metals consisting chieflyof alkali metals and aluminum having a porous volume (Vm) of 0.5 cc/g orlarger over the porous radii of from 200 to 1000 angstroms as measuredby a mercury porosimeter method, and a porous volume ratio as expressedby Vm/Vo of 30% or larger with respect to the whole porous volume (Vocc/g) or in an anion exchanger thereof.

According to the present invention, furthermore, there is provided apolyacetal resin composition obtained by blending said antistatic agentin an amount of from 0.1 to 40 parts by weight per 100 parts by weightof the polyacetal resin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning-type electron microphotograph of the structure ofgrains of a base material 6 obtained according to an Example of thepresent invention at a magnification of 30,000 times; and

FIG. 2 is a scanning-type electron microphotograph of the structure ofgrains of an antistatic agent (No. E-8) obtained according to an Exampleof the present invention at a magnification of 30,000 times.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, a distinguished feature resides inthat the antistatic agent is obtained by including polyalkylene polyolsor alkli metal salt-dissolved polyalkylene polyols in a basic carbonateof metals consisting chiefly of alkali metals and aluminum having aporous volume of 0.5 cc/g or larger over the porous radii of from 200 to1000 angstroms or in an anion exchanger thereof.

As will be demonstrated in Examples appearing later, the antistaticagent little causes the polyacetal resin to be thermally decomposed orto lose the mechanical strength even when it is blended in the resin ina considerably large amount and is melt-molded, contrary to theconventional ionic compounds which caused thermal decomposition andreduction in the mechanical strength without exception.

Moreover, the antistatic agent of the present invention exhibitsexcellent antistatic property even when it is blended in such a smallamount as 1 part by weight or less per 100 parts by weight of thepolyacetal resin, and this antistatic property is not quite lost evenwhen the surface of a resin molded article is wiped with methanol or thelike or even under low-humidity conditions.

With the conventional surfactant-type antistatic agents, the antistaticproperty was not obtained without the bleeding phenomenon on thesurface. By using the antistatic agent of the present invention,however, excellent antistatic property is obtained without the bleedingphenomenon.

Moreover, the antistatic agent of the present invention containscomponents which are all colorless (transparent) or white, and littlecauses the blended resin to be colored in a particular hue, andmaintains the molded article of resin in white color or enables themolded article of resin to be colored in any hue.

It is presumed that the antistatic property of the antistatic agent ofthe present invention is imparted through an ionic conduction mechanismthough it has not yet been fully clarified. It is considered that thecomponent that supports the ionic conduction is an alkali metalcomponent in a basic carbonate or in an anion exchanger thereof, or analkali metal salt dissolved in a small amount in polyalkylene polyols.The resin is not thermally deteriorated and is not colored by ioniccomponents despite there are contained such an alkali metal component(ionic component) and polyalkylene polyols. This fact is closely relatedto the inclusion structure in which polyalkylene polyols are included inthe basic carbonate or in an artion exchanger thereof.

That is, the basic carbonate or the anion exchanger thereof that servesas a base material has a hydroxyl group in the molecules, and exhibitslarge affinity to the polyalkylene polyol, and further has a porousvolume which is as large as 0.5 cc/g or more over a region of so-calledmeso pores or quasi-macro pores of porous radii of from 200 to 1000angstroms, and holds the polyalkylene polyol in the porous volume.

The inclusion structure is confirmed from a scanning-type electronmicrophotograph. The accompanying FIG. 1 is a scanning-type electronmicrophotograph showing the structure of grains of a basic carbonate(for details refer to Example 6 appearing later) used in the presentinvention, and FIG. 2 is an electron microphotograph showing thestructure of gains of an antistatic agent of the present inventionobtained by including a polyethylene glycol or the like in the basiccarbonate of FIG. 1. When they are compared together, it will beconfirmed that the grains in FIG. 2 are slightly spreading toward thea-axis and the b-axis though there is almost no change in the shape andstructure of the primary grains. Though the details are not known, it ispresumed that the base material of the present invention having alayer-like structure is forming primary grains in which unit layer-likestructures are laminated into several layers, a card house structure iseasily formed by the interlayer gap and by the van der Waals force ofgroups of relatively flat grains which are ultra-fine primary grains,and an organic compound such as a polyethylene glycol or the like iseffectively held in the gaps of meso porous size to quasi-macro poroussize of porous radii of from 200 to 1000 angstroms possessed by thegroups of primary grains.

It is presumed that when the antistatic agent of the present inventionis blended in the polyacetal resin, and is melted and molded, thepolyethylene glycol or the like in the inclusion grains elutes out in asuitable amount into a continuous resin layer, and the ionic conductiontakes place due to an alkali metal component via a medium such as thepolyethylene glycol.

As will become obvious from Examples and Comparative Examples describedlater, furthermore, it is presumed that the organic compound such as thepolyethylene glycol or the like is not included in the meso pores ormicro pores of smaller than 200 angstroms, and are easily occluded inmacro pores of larger than 1000 angstroms but easily escape therefromand art not stably held, causing the antistatic property to diminish anddeveloping such a trouble as bleeding out.

(Basic Carbonate or Ion Exchanger thereof)

The base material of the present invention comprises a basic carbonateof metals consisting chiefly of alkali metals and aluminum, or an anionexchanger thereof. The metals may further include alkaline earth metalssuch as magnesium, calcium and barium, and metal components of the groupIIB such as zinc and the like, in addition to the above-mentionedmetals.

Carbonate anions in the basic carbonate are many inorganic or organicanions such as sulfate ions, sulfite ions, ions of oxy acid ofphosphorus, hydrohalogenic acid, ions of perhalogenic acid, acetic acid,succinic acid, maleic acid, stoatic acid, adipic acid and alkylsulfonicacid, at least part of which being capable of exchanging ions. Theseanion exchangers can also be used for accomplishing the objects of thepresent invention. Anions should generally be carbonate ions from thestandpoint of thermal stability.

In general, the basic carbonate or the anion exchanger thereof has acomposition represented by the formula (1),

    Al.sub.x M.sub.y R.sub.z (OH).sub.6.a/nA.mH.sub.2 O

wherein M is an alkali metal, R is an alkaline earth metal, A is ananion, x is a number of from 0.6 to 3 and, particularly, from 1 to 3, yis a number of from

0 to 3 and, particularly, from 1 to 9, z is a number of from 0 to 2.4and, particularly, from 0 to 2, y+z is a number which is not 0, a is anumber of from 0 to 6 and, particularly, from 1 to 8, n is a valency ofanion A, and m is a number of not greater than 3.

Among them, it is desired that the atomic ratio x/y of aluminum to thealkali metal M is from 1 to 2 from the standpoint of thermal stabilityand antistatic property. Furthermore, it is desired that the equivalentratio OH/A of hydroxyl group to anion is from 1 to 3 from the standpointof antistatic properties and preventing bleeding.

The alkali metal components may be Li, Na and K. Among them, Li ispreferred from the standpoint of electric conductivity. It is of courseallowable to use Na and K though their electric conductivities areslightly inferior.

The basic carbonate and the ion exchanger thereof used in the presentinvention may be in the form of uniformly intimate compositions or finecrystals or crystals. Generally, however, finely crystalline one ispreferred from the standpoint of excellent dispersion.

A particularly preferred example of the basic carbonate may be analuminum lithium hydroxy carbonate which ideally has a chemicalstructure represented by the formula (2),

    [Al.sub.2 Li(OH).sub.6 ].sub.2 CO.sub.5.mH.sub.2 O

In this structure, Al³⁺ forms a gibbsite-type layer-like lattice of anoctahedral form in which a Li+ ion exists at a vacant lattice point. Thecomposition ratio can be changed depending upon the degree ofsubstitution for the vacant lattice points.

Another preferred example of the basic carbonate may be an aluminumsodium hydroxy carbonate which ideally has a chemical structurerepresented by the formula (3),

    AlNa(OH).sub.2 CO.sub.3.mH.sub.2 O

The basic carbonate used in the present invention is obtained byreacting a water-soluble aluminum salt, an alkali carbonate and, asrequired, a water-soluble alkaline earth metal salt at a predeterminedratio of amounts in the presence of an alkali hydroxide, and, asrequired, aging the formed co-precipitated products or further effectingthe hydrothermal treatment.

As the water-soluble aluminum salt, an aluminum chloride is particularlysuited but sulfate and nitrate can be used, too. As the alkalicarbonate, there can be used a lithium carbonate, a sodium carbonate anda potassium carbonate. As the alkaline earth metal a chloride can befavorably used, but a nitrate can be used, too. As the alkali hydroxide,a caustic soda can be used.

The reaction should be carried out in an aqueous medium and generallyunder the condition where a carbonate exists in excess amounts. Ingeneral, it is desired to carry out the reaction by adding a solutioncontaining a water-soluble aluminum salt and an alkaline earth metalsalt to the solution of the alkali carbonate and the alkali hydroxide.The reaction temperature should preferably be from 40° to 200° C.

The co-precipitated products are generally in the form of a uniformlyintimate composition or fine crystals, and can be used in their form toaccomplish the objects of the present invention. Generally, however, theco-precipitated products are aged in water heated at a temperature of60° to 100° C. to adjust the grain size, and are then used to accomplishthe objects of the present invention. The aged products can be furthersubjected to the aging processing at a high temperature (80° to 110° C.)and to the hydrothermal treatment at a temperature of 110° C. or higher,so that the products are precipitated in a more developed finecrystalline form or crystalline form.

It is desired that the basic carbonate or the anion exchanger thereofused in the present invention has a porous volume of 0.5 cc/g or largerand, particularly, 1.0 cc/g or larger over a region of meso porous sizeto quasi-macro porous size of porous radii of from 200 to 1000 angstromsas measured by the mercury manometric method.

Furthermore, it is desired that the basic carbonate or the anionexchanger thereof usually has a number average primary grain size offrom 0.05 to 1.0 μm and, particularly, from 0.05 to 0.5 μm as measuredby an electron microscope method, and further has a secondary grain size(median diameter) of from 0.5 to 10 μm and, more preferably, from 1 to 5μm and, particularly, from 1 to 9 μm as measured by a Couter countermethod.

Furthermore, the basic carbonate or the anion exchanger thereof may besubjected to an ordinary surface treatment in order to suppress thecoagulation and so that it can be dispersed in a polyacetal resin. Forinstance, fatty acid, an ester of fatty acid and a metal salt of fattyacid can be used as a surface treating agent.

(Antistatic Agent)

According to the present invention, the basic carbonate or the anionexchanger thereof is used as a base material and in which are includedpolyalkylene polyols or alkali metal salt-dissolved polyalkylenepolyols. Preferred examples of the polyalkylene polyols include apolyethylene glycol (PEG) as well as a polyoxyethylene-polyoxypropylenecopolymer, an ethylene glycol, a propylene glycol, a glycerin, apentaerythritol, an adduct of a polyhydric alcohol such as sorbitol andthe like and an ethylene oxide or a propylene oxide, and esters formedby fatty acids and an ethylene oxide or a propylene oxide.

The polyalkylene glycol may have a variety of molecular weights andshould usually have a number average molecular weight of 10000 orsmaller and, particularly, from 200 to 8000 from the standpoint ofelectric conductivity and anti-bleeding property in combination.

The polyalkylene glycols having various molecular weights can be usedbeing mixed together. Particularly excellent antistatic property isobtained when, for example, a polyalkylene glycol having a molecularweight of as small as from 100 to 1000, a polyalkylene glycol having anintermediate molecular weight of from 1000 to 3000 and a polyalkyleneglycol having a molecular weight of as large as from 3000 to 9000 areused being mixed at a weight ratio of 3-6:1-3:1-3.

The polyalkylene polyols should be contained in an amount of from 20 to110 parts by weight and, particularly, from 60 to 100 parts by weightper 100 parts by weight of the inorganic base material. When the amountis smaller than the above range, the antistatic property is notsufficient and when the amount is larger than the above range, thebleeding tends to develop.

It is allowable to use polyalkylene polyols in which an alkali metalsalt is dissolved instead of using polyalkylene polyols. Examples of thealkali metal salt include a lithium perchlorate, a lithium iodide, alithium trifluoromethane sulfonate, LiBF₄, a sodium iodide, NaCF₃ SO₃,KCF₃ SO₃, a lithium stearate, a sodium stearate, a zinc stearate, alithium maleate, a lithium succinate, a potassium succinate, a lithiumadipate and a lithium glycinate and the like. The alkali metal saltshould be used in an amount of from 1 to 20 parts by weight and,particularly, from 1.5 to 5 parts by weight per 100 parts by weight ofthe polyalkylene polyols.

Polyalkylene polyols or alkali metal salt-dissolved polyalkylene polyolsare included in the basic carbonate or in the anion exchanger thereof bydrying the basic carbonate or the anion exchanger thereof at atemperature of from 80° to 120° C., adding polyalkylene polyols whichare being melted (80° to 120° C.) to the powder heated at the abovetemperature, sufficiently mixing them together, and further mixing themtogether under a cooled condition. The mixture is stirred by using asuper mixer, a Henschel's mixer, a ball mill pulverizer, a rotarygranulator, a fluidized-bed granulator with a spray, a V-type mixingmachine, a double-shaft rotor type mixer, a ribbon-type mixer or aMuller type mixer.

(Polyacetal Resin Composition)

According to the present invention, the polyacetal resin is blended withthe above inclusion compound to impart excellent antistatic propertieswithout impairing other properties.

As the polyacetal resin used in the present invention, there can be usedeither a polyacetal homopolymer or a polyacetal copolymer in whichmajority portion of the main chain comprises an oxymethylene chain.

The antistatic agent of the present invention should be blended usuallyin an amount of from 0.1 to 40 parts by weight and, particularly, from1.0 to 30 parts by weight per 100 parts by weight of the resin, and theamount of blending can be selected depending upon the antistaticproperties that are required. Furthermore, a variety of widely knownstabilizers may be added to the composition of the present invention.

EXAMPLES

The present invention will be described more concretely by way ofExamples, but it should be noted that the invention is in no way limitedthereto only.

The antistatic agents of the present invention were mixed in amounts asshown in Tables 3, 4, 5 and 6 to 100 parts by weight of the polyacetalresin (produced by Polyplastics Co., trade name: DURACON M90) that isshown in Tables 4, 5 and 6. By using an extruder, the mixtures weremelted and kneaded to prepare pelletized compositions. The pellets wereinjection-molded to prepare test pieces which were then evaluated. Theresults were as shown in Tables 3, 4, 5 and 6. The following constituentcomponents were used for the Examples.

Antistatic Agent

Described below is a method of preparing an antistatic agent for thepolyacetal resins obtained by including polyols in a basic carbonateporous material (base material) of metals consisting chiefly of alkalimetals and aluminum and having meso pores.

(Base Material 1)

39.17 Grams of a sodium hydroxide and 11.16 g of a sodium carbonate wereadded to 1.0 l of water with stirring and were heated. Then, solutionsof a magnesium chloride, an aluminum chloride and an ammonium chloridewere gradually added thereto so that the molar ratio of Mg/Al was 2.0and the molar ratio of NH₃ /Al was 0.35, and a reaction slurry havingpH=10.2 was obtained. Then the reaction was carried out with stirring ata temperature of 40° to 90° C. for about 10 to 20 hours, followed by theaddition of about 3.3 g of a stearic acid, to effect the surfacetreatment with stirring. The reaction product was then filtered, washedwith water, dried at 70° C., and was pulverized using a small samplemill to obtain a base material 1.

(Base Materials 2 to 4)

Base materials 2, 3 and 4 were prepared in the same manner as that ofpreparing the base material 1, except that:

(1) the Mg/Al molar ratio was set to be 2.25, the NH₃ /Al molar ratiowas set to be 0.14, and stearic acid was added in an amount of 1.7 g;

(2) the Mg/Al molar ratio was set to be 3.00, the NH₃ /Al molar ratiowas set to be 0.14, and stearic acid was added in an amount of 1.5 g;and

(3) the (Mg+Zn)/Al molar ratio was set to be 2.25, MgCl₂ :ZnCl was setto be 9:1, and the NH₃ /Al molar ratio was set to be 0.14.

The base materials 1 to 4 were of the type of a hydrotalcite.

(Base Materials 5 and 6)

50.0 Grams of a sodium hydroxide and 14.9 g of a sodium carbonate wereadded to 4.0 l of water with stirring and were heated at 40° C. Then, asolution obtained by dissolving 18.66 g of Li₂ CO₃ and 99.56 g of AlCl₃in 0.8 l of water were gradually poured thereto, so that the CO₃ /Limolar ratio was 2.0 and the Al/Li molar ratio was 1.5, and a slurryhaving pH=10.7 was obtained. The slurry was then aged with stirring at atemperature of 80° to 100° C. for about 10 to 18 hours, and was equallydivided into two. To the one slurry was added 1.1 g of stearic acid toeffect the surface treatment with stirring. The slurry was thenfiltered, washed with water, dried at 70° C., and was pulverized using asmall sample mill to obtain a base material 5.

The other remaining slurry was subjected to the hydrothermal treatmentat 100° to 130° C. for 6 hours, and to the obtained reaction slurry wasadded 1.1 g of stearic acid to effect the surface treatment withstirring. The slurry was then filtered, washed with water, and was driedat 70° C. to obtain a base material 6.

(Base Material 7)

A base material 7 was obtained in the same manner as that of the basematerial 5 but adjusting the CO₃ /Li molar ratio to be 0.7 and the Al/Limolar ratio to be 2.0.

The base materials 5 to 7 possessed the chemical composition representedby the formula (2) described earlier.

(Base Material 8)

A base material 8 was obtained in the same manner as that of the basematerial 7 but adjusting the CO₃ /Na molar ratio to be 1.5 and Al/Namolar ratio to be 1.0 by using solutions of a sodium hydroxide, a sodiumcarbonate and an aluminum chloride, effecting the ripening at 90° to100° C. and effecting the hydrothermal treatment at 110° to 140° C. for6 hours.

The base material 8 possessed the chemical composition represented bythe formula (3) described earlier.

(Properties of the Base Materials and Method of Measuring theProperties)

Properties of the base materials were measured by the methods describedbelow, and the results were shown in Table 1.

Measuring Methods

1) Hunter's whiteness.

Measured by using an automatic reflection meter, Model TR-600manufactured by Tokyo Denshoku Co.

2) Oil absorption.

Measured in compliance with JIS K-5101.

3) Specific surface area.

Measured based on the BET method using Sorptomatic Series 1800 producedby CARLOERBA Co.

4) The sample dried in a constant-temperature drier at 150° C. for 8hours was accurately weighed in an amount of 0.5 g, and the whole porousvolume Vo over porous radii of from 75000 to 18 angstroms of the sampleand meso porous to quasi-macro porous volume Vm over porous radii offrom 200 to 1000 angstroms, were found by using a mercury manometricporosimeter (Model AG65 produced by CARLO ERBA Co.).

The ratio Rm of the meso porous to quasi-macro porous volume (volumeover meso porous to quasi-macro porous region) Vm relative to the wholeporous volume Vo was found in accordance with the following relation,

    Rm=Vm/Vo×100

5) Primary grain size.

By using a scanning electron microscope WET-SEM (WS-250) produced byAkashi Beam Technology Co., the primary grains in an image of a limitedvisible field were arithmetically averaged to find a primary grain size(μm).

6) Secondary grain size.

Measured by using a Couter counter, Model TA-II, produced by CouterCounter Co. The dispersion medium was ISOTON II which was a dispersionsolution for use exclusively in the Couter counter.

(Preparation of Inclusion Products)

Described below are antistatic agents of the present inventioncomprising inclusion products obtained by including polyalkylene polyolsor polyalkylene polyols/alkali metal salts in the above-mentioned basematerials 1 to 8.

(Antistatic Agent Group A)

The base materials 1, 4, 5, 6 and 8 were introduced each in an amount of500 g into a small super mixer of a capacity of 10 L, treated under theconditions of 400 rpm or lower and a temperature of 100° to 120° C. forone hour, and to which were mixed a polyethylene glycol (PEG) that wasmelted at 90° to 100° C. and a lithium salt dissolved in the molten PEGin amounts as shown in Tables 2 and 3, under the conditions of atemperature of 90° to 100° C. and 400 rpm. The mixtures were then mixedat a high speed of 1200 rpm, and were discharged from the mixer underthe conditions of a temperature of 60° C. or lower at 800 rpm in orderto obtain an antistatic agent group A.

(Antistatic Agent Group B)

An antistatic agent group B was obtained in the same manner as that ofthe antistatic agent group A but using the base materials 2, 6 and 7each in an amount of 500 g and using polyalkylene polyols other than thepolyethylene glycol in amounts as shown in Tables 2 and 3.

The recipes of the antistatic agents (E-1 to E-20) prepared according tothe above-mentioned method and used in the Examples were as shown inTables 2 and 3, and their antistatic properties were as shown in Tables4, 5 and 6. The resin molded products obtained in Examples 5, 23 and 26emitted the odor of formalin.

COMPARATIVE EXAMPLES

For the purpose of comparison as described below, other inorganic basematerials were used instead of the base materials of the presentinvention, the polyalkylene polyol only was used, the base material onlywas used, and known antistatic agents were used. The results were asshown in Tables 7 and 8.

(Comparative Examples H-1 to H-9)

(H-1)

Sedimentation-method silica having an oil absorption of 240 ml/100 g, amacro porous volume (hereinafter written as Ve) over porous radii ofgreater than 1000 angstroms of 2.3 cc/g and a BET specific surface areaof 230 m² /g, was impregnated with an organic compound in the sameamount as the antistatic agent E-8 of Table 2 under the same conditions.The silica possessed Vm=0.8 cc/g and Vm/Vo=20%.

(H-2)

An amorphous calcium silicate having an oil absorption of 10.0 ml/100 g,a Ve of 1.72 cc/g, a BET specific surface area of 95 m² /g, an averagesecondary grain size of 2 μm and a CaO/SiO₂ molar ratio of 0.8, wasimpregnated with an organic compound in the same amount as theantistatic agent E-3 of Table 2. The calcium silicate possessed Vm=0.5cc and Vm/Vo=18%.

(H-3)

An amorphous calcium silicate having an oil absorption of 270 ml/100 g,a Ve of 2.6 cc/g, a BET specific surface area of 320 m² /g, an averagesecondary grain size of 6 μm and a CaO/SiO₂ molar ratio of 0.7, wasimpregnated with an organic compound in the same amount as theantistatic agent E-3 of Table 2. The calcium silicate possessed Vm=0.4cc and Vm/Vo=17%.

(H-4)

To an aqueous slurry of a commercially available bayerite-type aluminumhydroxide having an average grain size of 1.8 μm were added, at atemperature of 40° C. with stirring, an aluminum chloride in an amountthat corresponds to 5 mol % of aluminum component, as well as a lithiumcarbonate and a lithium chloride in an amount that corresponds to 5 mol% of lithium component, so that the CO₃ /Li molar ratio was 2.0 and theAl/Li molar ratio was 1.5, and was further added a sodium carbonate sothat the pH of the slurry was 9.8. The mixture was treated with stirringat a temperature of 80° to 90° C. for about 6 hours, and was filtered,washed with water, dried and was pulverized to obtain a lithium/aluminumcomposite powder having the above composition.

This base material possessed an oil absorption of 85 ml/100 g, Vm=0.23cc/g, Ve=1.1 cc/g and Vm/Vo=16.5%.

Then, this powder was impregnated with 20 parts by weight of a PEG #200and 15 parts by weight of a PEG #400 per 100 parts by weight of thepowder in the same manner as in the Examples. Unlike the antistaticagent of the present invention, this agent appeared to be wet on thesurfaces of the grains.

Without using the base material, LiClO₄ was dissolved in PEG #200,PEG#2000 and PEG #6000 of amounts of the antistatic agent E-3 of Table2.

(H-6)

The base material 5 described in the Example was used.

(H-7, 8 and 9)

A glycerin monostearate, a sodium alkylsulfonate and an alkyleneammonium chloride were selected as the known surfactants.

(Items to be Evaluated and Evaluation Method)

Heat Decomposition Properties

During the melting and kneading in a biaxial extruder for preparingcomposition pellets, the decomposition phenomena (foaming,discoloration, formalin odor) of the molten mixture were totallyevaluated in five steps.

    ______________________________________                                        5         4          3     2        1                                         none      ← decomposition phenomenon →                                                          large                                           good                          poor                                            ______________________________________                                    

Mechanical Properties

The tensile strength was evaluated in compliance with the measuringmethod of ASTM D-638.

Antistatic Properties

A disk having a thickness of 3 mm and a diameter of 120 mm was preparedby the injection molding, and the surface resistivity and the halfperiod of charged voltage were evaluated.

In order to evaluate the stability in the antistatic property,furthermore, evaluation was effected right after the surfaces of themolded article was washed under the following conditions. To valuatedependency upon the environment, furthermore, the evaluation waseffected after the article was left under low-humidity conditions (23°C., 5% RH) for two days.

Surface resistivity: Measured by using ADVANTEST R8340 while applying avoltage of 500 V.

Half period of charged voltage: Measured by using Static Honestmetermanufactured by Shishido Shokai Co. while applying 6 kV.

Washing condition: Test pieces were submerged in methanol for 20 secondsand were dried by blowing off methanol on the surfaces with a nitrogengas.

                                      TABLE 1                                     __________________________________________________________________________         BET Whole                                                                     specific                                                                          porous                                                                            Meso porous to   Primary                                                                            Secondary                                       surface                                                                           volume                                                                            quasi-macro porous                                                                       Oil   grain                                                                              grain White-                               Base area                                                                              (Vo volume     absorption                                                                          size size  ness                                 material                                                                           (m.sup.2 /g)                                                                      cc/g)                                                                             Vm (cc/g)                                                                           Rm (%)                                                                             (ml/100 g)                                                                          (μm)                                                                            (μm)                                                                             (%) pH                               __________________________________________________________________________    1    32.4                                                                              3.29                                                                              1.36  41.33                                                                              62    0.10 3.50  94  9.5                              2    42.5                                                                              3.78                                                                              1.15  30.42                                                                              65    0.05 4.80  94  9.8                              3    31.0                                                                              3.24                                                                              1.28  39.51                                                                              57    0.10 2.70  95  10.0                             4    30.5                                                                              3.32                                                                              1.18  35.54                                                                              55    0.10 3.20  95  9.5                              5    25.3                                                                              2.25                                                                              1.10  48.89                                                                              55    0.20 2.50  94  8.5                              6    22.4                                                                              2.15                                                                              1.08  50.23                                                                              56    0.20 1.80  95  9.0                              7    27.8                                                                              2.37                                                                              1.15  48.52                                                                              60    0.15 4.70  94  8.4                              8    10.5                                                                              1.52                                                                              0.61  40.13                                                                              50    0.50 3.80  94  8.0                              __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    (Antistatic agent group A)                                                    Antistatic                                                                         Base                                                                     agent                                                                              material                                                                           Organic electrolyte. alkali salt                                    No.  No.  (parts by wt)/100 parts by wt of base material                      __________________________________________________________________________    E-1  1    PEG #200 (40.2)                                                                        PEG #2000 (13.4)                                                                       PEG #6000 (13.4)                                  E-2  5    PEG #200 (49.2)                                                                        PEG #2000 (16.4)                                                                       PEG #6000 (16.4)                                  E-3  5    PEG #200 (48)                                                                          PEG #2000 (16)                                                                         PEG #6000 (16)                                                                         LiClO.sub.4 (2)                          E-4  5    PEG #200 (48)                                                                          PEG #2000 (16)                                                                         PEG #8000 (16)                                                                         LiClO.sub.4 (2)                          E-5  5    PEG #200 (48)                                                                          PEG #2000 (14.5)                                                                       PEG #6000 (14)                                                                         Li stearate (5.5)                        E-6  5    PEG #200 (48)                                                                          PEG #2000 (15)                                                                         PEG #6000 (15)                                                                         Li laurate (4)                           E-7  6    PEG #200 (48)                                                                          PEG #2000 (16)                                                                         PEG #6000 (15.7)                                                                       Li maleate (2.3)                         E-8  6    PEG #200 (48)                                                                          PEG #2000 (16)                                                                         PEG #6000 (16)                                                                         LiClO.sub.4 (2)                          E-9  6    PEG #200 (48)                                                                          PEG #2000 (16)                                                                         PEG #6000 (15.4)                                                                       KClO.sub.4 (2.6)                          E-10                                                                              3    PEG #1000 (45)                                                                         PEG # 2000 (12)                                                                        PEG #4000 (12)                                                                         LiCF.sub.3 SO.sub.3 (3)                   E-11                                                                              4    PEG #1000 (40)                                                                         PEG #2000 (12.5)                                                                       PEG #4000 (12.5)                                                                       LiAlCl.sub.4 (2.5)                        E-12                                                                              2    PEG #2000 (23)                                                                         PEG #4000 (18.5)  LiClO.sub.4 (1)                           E-13                                                                              6    PEG #200 (42)                                                                          PEG #2000 (16.5)                                                                       PEG #6000 (16)                                                                         Li glycinate (1.5)                        E-14                                                                              8    PEG #200 (48)                                                                          PEG #2000 (16)                                                                         PEG #6000 (15)                                                                         NaCFl.sub.3 SO.sub.3 (3)                  E-15                                                                              7    PEG #4000 (40)             LiClO.sub.4 (0.8)                        __________________________________________________________________________

                  TABLE 3                                                         ______________________________________                                        (Antistatic agent group B)                                                            Base                                                                  Antistatic                                                                            material Organic electrolyte. alkali salt (parts                      agent No.                                                                             No.      by wt)/100 parts by wt of base material                      ______________________________________                                        E-16    5        polyoxyethylenemonooleyl ether                                                                    LiClO.sub.4                                               (BO-20 produced by Nikko                                                                          (2)                                                       Chemicals Co.) (50)                                          E-17    5        polyoxyethylene monostearate                                                                      LiBF.sub.4                                                (Noinion S15.4 produced Nippon                                                                    (2)                                                       Yushi Co.) (50)                                              E-18    5        polyoxyethyleneglycerin                                                                           LiBF.sub.4                                                monostearate (Rikemal S-120,                                                                      (2)                                                       produced by Riken Vitamin Co.)                                                (50)                                                         E-19    5        polyoxyethylenesorbitan                                                                           LiClO.sub.4                                               monooleate (TO-10M, produced                                                                      (2)                                                       by Nikko Chemicals Co.) (50)                                 E-20    5        polyoxyethylene-oxypropylene                                                                      LiClO.sub.4                                               copolymer (Planon 208, produced                                                                   (2)                                                       by Nippon Yushi Co.) (50)                                    ______________________________________                                    

                                      TABLE 4                                     __________________________________________________________________________                 Example No.                                                                   1    2    3    4    5    6    7    8    9    10                  __________________________________________________________________________    Polyacetal resin                                                                           100  100  100  100  100  100  100  100  100  100                 (DURACON M90-44)                                                              (parts by weight)                                                             Antistatic agent No.                                                                       E-1  E-2  E-3  E-4  E-5  E-6  E-7  E-8  E-9  E-10                (parts by weight)                                                                          (5)  (5)  (5)  (5)  (5)  (5)  (5)  (5)  (5)  (5)                 Heat decomposition                                                                         5    5    5    5    4    5    5    5    5    5                   properties                                                                    Tensile strength (Kgf/cm.sup.2)                                                            578  575  580  581  572  575  575  580  579  570                 Antistatic properties                                                         Before washing                                                                Surface resistance (Ω)                                                               2.7E+13                                                                            2.6E+13                                                                            1.8E+12                                                                            1.8E+12                                                                            4.0E+12                                                                            3.2E+12                                                                            3.7E+12                                                                            2.5E+12                                                                            6.7E+12                                                                            9.7E+12             Half-life electrification                                                                  23.3 21.2 3.5  4.1  10.1  8.7  9.2  8.9 14.8 17.2                (sec)                                                                         After washing                                                                 Surface resistance (Ω)                                                               3.2E+13                                                                            4.7E+13                                                                            2.7E+12                                                                            2.8E+12                                                                            4.5E+12                                                                            3.7E+12                                                                            4.2E+12                                                                            3.7E+12                                                                            8.3E+12                                                                            1.4E+13             Half-life electrification                                                                  25.8 29.2 5.3  4.9  13.2 10.7 12.8 11.0 16.0 18.1                (sec)                                                                         Low humidity                                                                  Surface resistance (Ω)                                                               4.9E+13                                                                            4.6E+13                                                                            3.3E+12                                                                            2.9E+12                                                                            4.8E+12                                                                            3.7E+12                                                                            6.5E+12                                                                            1.1E+13                                                                            9.5E+12                                                                            1.3E+13             Half-life electrification                                                                  38.2 30.0 9.0  7.8  12.7 12.1 14.0 14.7 17.0 17.9                (sec)                                                                         __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________                 Example No.                                                                   11   12   13   14   15   16   17   18   19   20                  __________________________________________________________________________    Polyacetal resin                                                                           100  100  100  100  100  100  100  100  100  100                 (DURACON M90-44)                                                              (parts by weight)                                                             Antistatic agent No.                                                                       E-11 E-12 E-13 E-14 E-15 E-16 E-17 E-18 E-19 E-20                (parts by weight)                                                                          (5)  (5)  (5)  (5)  (5)  (5)  (5)  (5)  (5)  (5)                 Heat decomposition                                                                         5    5    5    5    5    5    5    5    5    5                   properties                                                                    Tensile strength (Kgf/cm.sup.2)                                                            583  587  578  569  555  577  576  588  585  581                 Antistatic properties                                                         Before washing                                                                Surface resistance (Ω)                                                               1.5E+13                                                                            4.5E+13                                                                            1.0E+13                                                                            8.8E+12                                                                            1.4E+13                                                                            6.9E+12                                                                            8.8E+12                                                                            3.7E+12                                                                            6.8E+12                                                                            5.3E+12             Half-life electrification                                                                  19.6 32.9 15.8 14.2 20.0 11.2 15.3 10.1 14.2 12.1                (sec)                                                                         After washing                                                                 Surface resistance (Ω)                                                               1.7E+13                                                                            5.2E+13                                                                            1.1E+13                                                                            8.9E+12                                                                            1.7E+13                                                                            7.3E+12                                                                            8.8E+12                                                                            6.2E+12                                                                            7.2E+12                                                                            6.4E+12             Half-life electrification                                                                  21.0 34.2 16.2 16.1 21.0 14.4 15.7 15.1 15.8 14.3                (sec)                                                                         Low humidity                                                                  Surface resistance (Ω)                                                               2.3E+13                                                                            5.7E+13                                                                            1.9E+13                                                                            9.3E+12                                                                            3.8E+13                                                                            9.5E+12                                                                            1.7E+13                                                                            7.2E+12                                                                            1.0E+13                                                                            8.9E+12             Half-life electrification                                                                  24.8 38.3 20.8 17.0 26.7 19.8 20.3 16.3 14.8 16.5                (sec)                                                                         __________________________________________________________________________

                                      TABLE 6                                     __________________________________________________________________________                   Example No.                                                                   21   22   23   24   25   26                                    __________________________________________________________________________    Polyacetal resin (DURACON                                                                    100  100  100  100  100  100                                   M90-44) (parts by weight)                                                     Antistatic agent No.                                                                         E-3  E-3  E-3  E-8  E-8  E-8                                   (parts by weight)                                                                            (0.5)                                                                              (10) (30) (0.5)                                                                              (10) (30)                                  Heat decomposition properties                                                                5    5    4    5    5    4                                     Tensile strength (Kgf/cm.sup.2)                                                              613  555  409  609  560  393                                   Antistatic properties                                                         Before washing                                                                Surface resistance (Ω)                                                                 3.9E+13                                                                            1.9E+11                                                                            7.3E+10                                                                            3.2E+13                                                                            3.2E+11                                                                            5.5E+10                               Half-life electrification                                                                    26.1 <1   <1   42.1 <1   <1                                    (sec)                                                                         After washing                                                                 Surface resistance (Ω)                                                                 4.3E+13                                                                            2.3E+11                                                                            1.2E+11                                                                            6.1E+13                                                                            3.2E+11                                                                            5.7E+10                               Half-life electrification                                                                    31.8 <1   <1   49.3 <1   <1                                    (sec)                                                                         Low humidity                                                                  Surface resistance (Ω)                                                                 4.9E+13                                                                            9.4E+11                                                                            1.5E+11                                                                            4.9E+13                                                                            3.1E+11                                                                            6.9E+10                               Half-life electrification                                                                    42.4 1.3  <1   32.0 1.9  <1                                    (sec)                                                                         __________________________________________________________________________

                                      TABLE 7                                     __________________________________________________________________________                   Comparative Example No.                                                       1  2  3  4    5    6                                           __________________________________________________________________________    Polyacetal resin (DURACON                                                                    100                                                                              100                                                                              100                                                                              100  100   100                                        M90-44) (parts by weight)                                                     Antistatic agent No. or name                                                                 E-1                                                                              E-2                                                                              E-3                                                                              E-4  E-5  E-6                                         (parts by weight)                                                                            (5)                                                                              (5)                                                                              (5)                                                                              (5)  (5)  (5)                                         Heat decomposition properties                                                                 1  2  1  3    3     3                                         Tensile strength (Kgf/cm.sup.2)                                                              -- -- -- 521  492   589                                        Antistatic properties                                                         Before washing                                                                Surface resistance (Ω)                                                                 -- -- -- 4.9E+12                                                                            3.2E+12                                                                            1.4E+15                                     Half-life electrification (sec)                                                              -- -- --    9.8                                                                               12.8                                                                             >150                                        After washing                                                                 Surface resistance (Ω)                                                                 -- -- -- 6.7E+13                                                                            4.5E+13                                                                            1.1E+15                                     Half-life electrification (sec)                                                              -- -- --   48.2                                                                               28.6                                                                             >150                                        Low humidity                                                                  Surface resistance (Ω)                                                                 -- -- -- 2.1E+13                                                                            3.7E+12                                                                            2.9E+15                                     Half-life electrification (sec)                                                              -- -- --   24.5                                                                               12.1                                                                             >150                                        Remarks        A  A  A  B    C    strong                                                                        formlin odor                                __________________________________________________________________________     A: considerably decomposed during extrusion and could not be pelletized       B: strong formalin odor. bleed on the article surface (2 days after           molded)                                                                       C: strong formalin odor. conspicuous beelding on the article surface (2       days after molded)                                                       

                                      TABLE 8                                     __________________________________________________________________________                   Comparative Example No.                                                       7      8    9         10                                       __________________________________________________________________________    Polyacetal resin (DURACON                                                                    100    100  100        100                                     M90-44) (parts by weight)                                                     Antistatic agent No. or name                                                                 E-7 (5)                                                                              E-8 (5)                                                                            E-9 (5)   --                                       (parts by weight)                                                                            glycerine                                                                            Na alkyl-                                                                          Cl alkylene                                                       monostearate                                                                         sulfonate                                                                          ammonium chloride                                  Heat decomposition properties                                                                 4      1    1          5                                      Tensile strength (Kgf/cm.sup.2)                                                              520    --   --         620                                     Antistatic properties                                                         Before washing                                                                Surface resistance (Ω)                                                                 5.6E+11                                                                              --   --        1.7E+15                                  Half-life electrification (sec)                                                                 1.0 --   --        >150                                     After washing                                                                 Surface resistance (Ω)                                                                 1.6E+15                                                                              --   --        2.0E+15                                  Half-life electrification (sec)                                                              150    --   --        >150                                     Low humidity                                                                  Surface resistance                                                                           7.1E+13                                                                              --   --        2.5E+15                                  Half-life electrification (sec)                                                                40.3 --   --        >150                                     Remarks        A      B    B                                                  __________________________________________________________________________     A: conspicuous bleeding on the article surface (2 days after extrusion        molding)                                                                      B: considerably decomposed during extrusion and could not be pelletized  

As will be obvious from the foregoing description and Examples, theantistatic agents of the present invention impart very good antistaticproperties to the polyacetal resins, and the antistatic properties arenot lost even after the surfaces of the resins are washed with solventsor even under the low-humidity conditions.

Moreover, the antistatic agents of the present invention do not almostpermit the thermal properties and the mechanical properties to bedeteriorated, that was the problem with the conventional knownantistatic agents.

Owing to the above-mentioned properties, the polyacetal resincompositions of the present invention can be extensively used in thefield of engineering plastics where the polyacetal resins haveheretofore been used.

We claim:
 1. A polyacetal resin composition obtained by blending anantistatic agent comprising an inclusion product obtained by includingpolyalkylene polyols or alkali metal salt-dissolved polyalkylene polyolsin a basic carbonate of metals consisting chiefly of alkali metals andaluminum having a porous volume (Vm) of 0.5 cc/g or larger over theporous radii of from 200 to 1000 angstroms as measured by a mercuryporosimeter method, and a porous volume ratio as expressed by Vm/Vo of30% or larger. wherein Vo (cc/g) is the whole porous volume or in ananion exchanger thereof, in an amount of from 0.1 to 40 parts by weightper 100 parts by weight of the polyacetal resin.
 2. The polyacetal resincomposition of claim 1, wherein the basic carbonate of metals consistingchiefly of alkali metals and aluminum or the anion exchanger thereof hasa chemical composition represented by the formula (1),

    Al.sub.x M.sub.y R.sub.z (OH)6.a/nA.mH.sub.2 O

wherein x is a number of from 0.6 to 3, y is a number of from 0 to 3, zis a number of from 0 to 2.4, y+z is a number which is not 0, a is anumber of from 0 to 6, M is an alkali metal, R is an alkaline earthmetal, A is an anion, n is a valency of anion A, and m is a number ofnot greater than
 3. 3. The polyacetal resin composition of claim 1,wherein polyalkylene polyols or alkali metal salt-dissolved polyalkylenepolyols are included in the antistatic agent in the amount of 20 to 110parts by weight per 100 parts by weight of the basic carbonate or theanion exchanger thereof.
 4. The polyacetal resin composition of claim 1,wherein the alkali metal salt-dissolved polyalkylene polyols of theantistatic agent are those in which the alkali metal salts are dissolvedin amounts of from 1 to 20 parts by weight per 100 parts by weight ofthe polyalkylene polyols.
 5. The polyacetal resin composition of claim1, wherein the basic carbonate of the antistatic agent is an aluminumlithium hydroxycarbonate.
 6. The polyacetal resin composition of ofclaim 1, wherein the basic carbonate of the antistatic agent is analuminum sodium hydroxycarbonate.
 7. The polyacetal resin composition ofclaim 1, wherein the polyalkylene polyols of the antistatic agent arepolyethylene glycols.
 8. The polyacetal resin composition of claim 1wherein the polyacetal resin a polyacetal homopolymer in which themajority portion of the main chain comprises an oxymethylene chain. 9.The polyacetal resin composition of claim 1 wherein the polyacetal resinis a polyacetal copolymer in which the majority portion of the mainchain comprises an oxymethylene chain.
 10. The polyacetal resincomposition of claim 1 obtained by blending the antistatic agent in anamount of from 1.0 to 30 parts by weight per 100 parts by weight of thepolyacetal resin.